This invention relates to automotive vehicle inspection and maintenance equipment. The invention is especially adapted for inspecting and maintaining the emission control system and emissions or exhaust components of a vehicle. More particularly, the invention concerns the accurate measurement of gases emitted in a vehicle's exhaust in loaded mode testing.
In an effort to reduce the concentrations of hydrocarbons (HC), carbon monoxide (CO) and carbon dioxide (CO.sub.2), inspection and maintenance (I/M) programs have been established at the national and state level to ensure that emissions of each vehicle are below a prescribed level. One problem with such I/M programs is that most tests are performed with the vehicle unloaded, i.e., with the engine disengaged from the drive wheels. A study commissioned by the California B.A.R. found that a comparison between an unloaded engine at 2500 rpm and the Federal Test Program (FTP), established a correlation of only 0.49 for HC and 0.75 for CO. The correlation was much worse when the unloaded engines were tested at idle speed.
An improved testing correlation with FTP is provided by loaded-mode testing on a dynomometer However, the cost of installing dynomometers at all I/M test facilities in even one state would be prohibitive. Also, there remains a need for gas emission testing of vehicles in independent repair shops in order for the mechanic to verify the success of the repair procedure prior to sending the vehicle back to the I/M test facility. The prohibitive cost of dynomometers for I/M test facilities is magnified when contemplated for every independent repair shop which, in some states, also perform I/M testing.